This invention relates to treating of naphtha to prepare aromatic hydrocarbons. More particularly it relates to a process for treating a pyrolysis naphtha.
As is well known to those skilled in the art, the shortage of gasoline has resulted in the need to seek greater yields of gasoline from existing stocks and/or the need to upgrade various feedstocks which have a high content of high octane components. Typical of such components are various pyrolysis naphtha streams including those recovered as by-products from thermal cracking of various charge materials including paraffin charge stocks. A commonly available pyrolysis naphtha is the steam cracked naphtha derived as a byproduct of the production of ethylene by thermal steam cracking of naphtha charge.
Pyrolysis (including thermally steam cracked) naphtha, commonly referred to as dripolene, includes the liquid byproducts of thermal steam cracking and contains 80%-90% of 5-8 carbon hydrocarbons plus 10%-20% of hydrocarbons having at least 9 carbon atoms. Generally neither fraction is passed to the gasoline pool without further treatment since they contain gums (or more accurately components which form gums during heat treatment or distillation). Typically dripolene may contain such materials in amount of 0.1%-0.5%.
These gum forming materials include a wide variety of hydrocarbons generally containing olefinic double bonds. Such components may include alkyl aromatics (e.g. styrenes), fused ring compounds (e.g. indenes), and diolefins. Most of these components may be olefins or diolefins.
These ingredients contribute to the foul odors, low volatilities, poor stability, low octane values, high gum content, etc. attributed to dripolenes.
Prior art techniques have attempted to convert dripolene or dripolene derived compositions to useful products which are free of the disadvantages derived from the noted compositions.
It is an object of this invention to provide a process for treating pyrolysis naphthas, such as dripolenes. Other objects will be apparent to those skilled in the art.